A semiconductor chip having high withstand voltage and large current capacity generates large heat while operating. Therefore, it is required to improve heat radiation radiated from the chip. In view of the heat radiation, a semiconductor device having a large current semiconductor chip is disclosed in Japanese Patent Application Publication No. 2003-110064 (i.e., U.S. Patent Application Publication No. 2003-0022464-A1). The semiconductor device includes a pair of heat sinks made of metal, which are disposed on both sides of the semiconductor chip through a solder layer. Specifically, the heat sinks are bonded to the semiconductor chip with the solder layer. Thus, the heat generated in the chip is radiated from both sides of the chip through the heat sinks. Therefore, the heat radiation efficiency is improved. Here, the semiconductor device having the heat sinks is molded with resin. However, the outside surface of each heat sink is exposed from the resin mold so that the heat radiation efficiency becomes effectively.
In the above semiconductor device, each thermal expansion coefficient of the semiconductor chip, the heat sink and the resin mold is different each other. Therefore, a large heat stress is generated at each bonding portion between them. The large heat stress may crack the chip. To protect the chip, the thickness of the chip is thinned so that a distortion at the bonding portion between the chip and the solder layer becomes small.
However, in the above semiconductor device, dimensions and shape of the heat sink are not defined. Therefore, a strain in the solder layer disposed between the chip and the heat sink may be increased so that the bonding member cracks by the strain.